1) Field of the Invention
The present invention relates to a system and method for ejecting stores and, more particularly, to a store ejection system and method that use a pressure vessel of pressurized non-pyrotechnic gas for providing the source of energy and the transfer mechanism to eject the stores.
2) Description of Related Art
The term “store” is used herein to refer generally to any of a number of munitions or other materials that can be dispensed from an aircraft, submarine, or other vehicle. For example, military aircraft can include a store ejection system to dispense bombs, missiles, rockets, and other types of munitions. Non-munitions stores can include electronic equipment and other materials. Typically, the store ejection system includes one or more racks beneath the wings or fuselage of the aircraft for holding the stores and releasing the stores upon a command. For example, store racks are described in U.S. Pat. Nos. 5,907,118 and 6,035,759, both by the same inventor and assignee as the present invention.
In one conventional store ejection system, the stores are connected to the racks by one or more mechanical hooks. The store ejection system includes a release mechanism for actuating the hooks to release the stores and a jettison mechanism for forcibly ejecting the stores away from the aircraft. The jettison mechanism can include a pressure-actuator, such as a ram that is actuated by a pressure increase in a cylinder. In the conventional system, the pressure is generated by a pyrotechnic cartridge, i.e., an explosive. Ignition of the pyrotechnic cartridge initiates a chemical reaction that generates a high pressure, which can be used for actuating the release mechanism and the jettison mechanism.
Although such pyrotechnic cartridges provide a weight efficient unit for storing and releasing energy, the cartridges present a number of maintenance, reliability, and safety concerns. For example, the chemical reaction of the explosive charge in the cartridge generates a large amount of residue. Some of the residue is deposited in the ejection system where it can clog or otherwise interfere with the components of the ejection system. Moisture and corrosives in the residue can also damage the ejection system. Additionally, moisture deposited in the ejection system can freeze or gather additional debris. To avoid unreliability and possible failure, the ejection system must be disassembled and cleaned regularly, thus increasing the cost and downtime for maintaining the system. Such cleaning often requires the use of hazardous cleaning solvents that require care in storage, use, handling, and disposal. Further, due to the pyrotechnic nature of the cartridges, special storage and handling precautions for the cartridges are necessary. For example, ground crew personnel must use special equipment to conduct stray voltage checks before installing the cartridges to prevent inadvertent firing. Also, unspent cartridges must be removed before unloading unreleased stores from the aircraft.
Non-pyrotechnic ejection systems have been proposed, such as the pneumatically-driven store ejection system described in U.S. Pat. No. 5,583,312, which is also by the same inventor and assignee as the present invention. That device does not require pyrotechnic cartridges, but instead includes a compressor for compressing a non-pyrotechnic gas that is then used to actuate ejector pistons of one or more suspension and release equipment (S & RE) modules that releasably retain and jettison stores. The pressurized gas, which can comprise ambient air, does not deposit a significant amount of residue on the system components. Thus, the residue build-up and corrosion resulting from pyrotechnic chemicals are eliminated and the maintenance required on the system is minimized. However, the compressor adds to the initial cost of the system and the recurring costs for overhauling and maintaining the compressor. The compressor also adds to the overall weight of the system. Further, the compressor requires the availability of sufficient power from the aircraft's electrical or hydraulic systems to drive the compressor motor. In addition, the compressor must generate sufficient pressure to release the stores, so the compressor requires an interval of time for preparing the release of the store. The time required to achieve a sufficient pressure is dependent on the compressor, the number and size of ejector racks that are connected to the system, and the air density, which varies with altitude. Therefore, the release of the stores can be delayed while the compressor generates the required pressure.
There have also been proposed ejector devices that use a stored volume of compressed gas to provide the energy for ejection. For example, U.S. Pat. Nos. 4,095,762 and 4,905,568 to Holt and Hetzer et al., respectively, each describe an ejector mechanism that uses a pressurized gas as the energy source for ejection and a hydraulic fluid, which acts as the energy transfer mechanism for ejection. Both patents describe that the hydraulic fluid can be used to re-pressurize the gas after ejection. Holt specifies that the action of recocking a piston moves the hydraulic fluid and thereby re-pressurizes the gas. Hetzer recites that after ejection, a pump is used to pump the hydraulic fluid, and the hydraulic fluid thereby acts on the gas to re-pressurize it. Therefore, neither patent requires a compressor for re-pressurizing the gas. However, the hydraulic systems add weight and complexity to the ejector device. Further, the pump of Hetzer for pumping the hydraulic fluid adds weight, power, and timing concerns similar to those discussed above in connection with the compressor of U.S. Pat. No. 5,583,312. Similarly, in the case of Holt, some additional device would be required for recocking the system.
U.S. Pat. No. 4,204,456 to Ward discloses a pneumatic bomb ejector that uses a pressurized gas from a storage container for the energy required to eject the bomb. However, no specific storage container is described, and there is no description regarding how and when the storage container is pressurized. Pressurizing the container during flight would require a pressurization device, such as a compressor, again with the weight, power, and timing concerns noted above. Alternatively, if the storage container is pre-pressurized before the aircraft takes off so that no on-board compressor is needed, the pressure in the storage container will fluctuate as the temperature of the gas in the storage container changes with the ambient temperature. Further, the pressure in the storage container will not be affected by changes in the ambient pressure. Thus, the differential in pressure between the storage container and the ambient air will change as the aircraft changes altitude, thereby changing the operational characteristics of the ejector and possibly resulting in incorrect or failed ejections. Additionally, refilling the container before take-off would require that the container be connected to a refilling device, which could delay the flight. Additional maintenance of the container, such as inspection or repair, would also add to the cost of operation and could increase the time required for on-ground preparation before flight.
Thus, there is a need for a store ejection system and method that use a non-pyrotechnic gas as the source of energy and transfer mechanism for jettisoning a store from an aircraft, submarine, or other vehicle. The system should not require the use of pyrotechnic reactions or an on-board compressor system, and maintenance required for providing the non-pyrotechnic gas should be minimized. Preferably, the system should not require a long time delay to achieve pressurization. Additionally, the system should require little or no power from the vehicle's electrical or hydraulic systems for pressurizing the gas.